DESCRIPTION (Taken from application) The goal of this project is to better understand the genotoxic effects of chromium and arsenic in mammals, when these metals are introduced either alone, or combined with benzo[a]pyrene. The research design employs a battery of novel mouse strains designed to detect frameshift and recombination events. One set of such mice uses a human PLAP (Placental Alkaline Phosphatase) gene. The PLAP gene was rendered inactive by insertion of 7 G:C basepairs. The frameshifted PLAP transgene is transcribed ubiquitously in all mouse tissues. Consequently, when the frameshift mutation in the PLAP transgene reverts, active PLAP enzyme is produced and deposited on the surface of the cell, where it is detected by a histochemical stain. This approach provides information about where mutant cells arise in different tissues. Mice that use PLAP expression to detect deletional recombination between direct repeats (PLAP-del mice) are under construction. While the PLAP-del mice are being developed, interstitial deletion after exposure to metals will be studied in a mouse strain called pink-eyed unstable. These mice have been used to show that sodium arsenate can induce recombination in mice. However, pink-eyed unstable mice can detect recombination in embryonic premelanocytes only. By contrast, the PLAP-del system reports recombination in all tissues. We will also study mitotic recombination by using another mouse strain we have developed. These mice are heterozygous for the aprt gene. Lymphocytes derived from cells that have undergone mitotic recombination at any point between aprt and the centromere on chromosome 8 can be selected because such cells lack APRT function and survive in 2, 6 diaminopurine. We propose to test the following hypotheses: 1) Chromium and arsenic induce frameshift mutations and homologous recombination in the cells of diverse tissues of mice. 2) Combining one or another of these metals with benzo[a]pyrene has a synergistic effect on mutation.